1. Field of the Invention
The present invention relates to target density detection using discrete photon counting. More particularly, the present invention relates to using discrete photon counting to produce transmission radiographic images of a target object with improved spatial resolution and high system sensitivity.
2. Background
There are many instances in the security or customs field when it is necessary to examine or inspect in a non-destructive way, the contents of a target object, such as a closed package, box, suitcase, cargo container, automobile semi-trailer, tanker truck, railroad car, e.g., box car or tanker car, or the like. For example, customs departments are routinely charged with the responsibility of inspecting vehicles coming into a country to make sure such packages do not contain drugs or other contraband, or leaving the country with stolen automobiles, drug money, and other illicit contraband. Similarly, drug smugglers frequently carry out their criminal acts by hiding illegal drugs in vehicles such as tanker trucks, and then sending the trucks through a border checkpoint. When security personnel encounter suspicious vehicles or other containers being transported over international boundaries, they must perform a careful time consuming (˜½ hour) inspection of such vehicles to ascertain their contents. Similarly, when suspicious trucks or cars enter compounds overseas having U.S. troops or containing embassy offices, they must be inspected for hidden vehicle bombs, poisonous gases, etc.
When suspicious vehicles are discovered, they generally must be examined or inspected on location in what is referred to as a “secondary inspection area.” If secondary inspection reveals the presence of contraband (e.g., drugs), then the vehicle may be impounded, the driver arrested, and the contraband disposed of. If, on the other hand, the examination reveals the absence of contraband, then the vehicle may be allowed to proceed in normal manner.